====== ohm_gl_fix — Phase 1 goal formulation, 2026-04-30 ======

Phase 1 of iteration 1. Index: [[ohm_gl_fix:start]]. Origin:
[[fourier:phase5_2026-04-30|fourier Phase 5 review handover, 2026-04-30]]
— that page identified Mali EGLImage import cost as the binding
constraint on the browser-side GL consumer; ohm_gl_fix is the campaign
that addresses it directly rather than via browser-side carrier
patches.

===== Phase 1 — Goal =====

On ''bbb_1080p30_h264.mp4'' (SHA-16 ''dcf8a7170fbd49bb''), with
''mpv --hwdec=v4l2request --vo=gpu-next'', over a 60 s steady-state
window, reduce frame drops from the baseline **1039 / 1440 (72 %)**
to within the transient-startup floor measured on the working
''gst v4l2slh264dec → waylandsink'' control path on the same clip
and window.

Equivalent framing: **EGLImage-import cost ceases to be the binding
constraint on per-frame budget on Mali-G52 / RK3566.**

==== Why this framing ====

  * **"Within the transient-startup floor" instead of literal zero.**
    mpv's gpu-next path drops a handful of frames at preroll while
    format negotiation, decoder priming, and first GLES texture
    allocation settle. The ''gst → waylandsink'' control path drops
    0 / 1440 today, so the realistic floor is 0–N where N is the
    post-fix steady-state count after preroll. Locking the goal to
    the control-path floor keeps it falsifiable without being
    unreachably literal.
  * **"Binding constraint" instead of a CPU% number.** A CPU% target
    presumes a particular ratio of import cost to composite cost. If
    a partial fix unmasks libplacebo composite or NV12→RGB shader
    fillrate as the new bottleneck, the goal as written still answers
    ("did import stop binding the budget?") rather than re-litigating
    the metric.
  * Phase 3 will validate or invalidate this hypothesis. Loop edge
    3→1 stays open per ''feedback_dev_process.md''.

===== Constraints (Phase 3 / 4 review criteria, not the goal itself) =====

  * No dropped safety checks. Question redundant per-frame validations
    where buffer identity is already established at both ends; do not
    eliminate end-of-pipe sanity checks.
  * Prefer pointer / fd passing over buffer copies wherever a copy is
    found. EGLImage caching keyed by dmabuf fd identity is the
    structural fix this implies; per-frame fresh-import is the
    structural waste.
  * Patches and changes must be aligned to upstream in syntax and
    semantics. No upstream submissions (PRs/MRs/bug reports) without
    explicit task; flagging upstream-worthy work to Markus is welcomed
    with a why.
  * Scope per ''~/src/ohm_gl_fix/README.md'': panfrost
    EGLImage-from-dmabuf for NV12 with Rockchip-relevant DRM modifiers
    + EGLImage caching across V4L2 buffer-pool reuse. Out: V4L2
    decoder work (fourier), browser carriers (fourier), compositor
    overlay-plane promotion, Vulkan video.

===== Test discipline =====

  * **Primary clip + config (locked):** ''bbb_1080p30_h264.mp4''
    (SHA-16 ''dcf8a7170fbd49bb''),
    ''mpv --hwdec=v4l2request --vo=gpu-next'', 60 s window.
  * **Control path (locked):** ''gst-launch-1.0'' v4l2slh264dec →
    waylandsink, paced ''sync=true'', 60 s window — used to define
    the transient-startup floor.
  * **Generalisation clip (Phase 6 if primary is met):** named in
    Phase 4. 1080p60 H.264 is the candidate; locking choice once
    Phase 2 + 3 expose any clip-class sensitivity in the import
    path.

===== Source artefacts =====

  * Campaign README: ''~/src/ohm_gl_fix/README.md''
  * Origin freeze: [[fourier:phase5_2026-04-30|fourier Phase 5 review handover]]
  * Process spec: ''feedback_dev_process.md'' — the 8-phase loop
  * Sibling project: [[fourier:start]]

----

//Phase 1 entry locked 2026-04-30 after a goal-vs-constraint
separation review with Markus. Phase 2 (situation analysis) is the
next entry.//